Lightsabers work like any other weapon, just like in most MMOs, console games, etc. They have a damage factor per hit and follow combat rules like other weapons. There's no such thing as them automatically slicing someone in half or whatever you're imagining for some reason.

Cortosis, phrik, beskar, ultrachrome, neutronium, darkswords, Bane's parasites the name of which I can't remember right now, any objects imbued with Force Weapon, any objects created or altered by Sith Alchemy, probably some more stuff I can't remember.

This list is from memory, it's been a while since I've been on Wookieepedia. Regardless though, the rarity of the materials combined with the nature of damage in a game means that most likely all weapons will have a measure of resistance against a lightsaber.